diff --git a/pkgs/development/ruby-modules/gem/default.nix b/pkgs/development/ruby-modules/gem/default.nix
index 03f8b10aacce..158d5891ec3a 100644
--- a/pkgs/development/ruby-modules/gem/default.nix
+++ b/pkgs/development/ruby-modules/gem/default.nix
@@ -205,8 +205,11 @@ stdenv.mkDerivation ((builtins.removeAttrs attrs ["source"]) // {
       $gempkg $gemFlags -- $buildFlags
 
     # looks like useless files which break build repeatability and consume space
-    rm -fv $out/${ruby.gemPath}/doc/*/*/created.rid || true
-    rm -fv $out/${ruby.gemPath}/gems/*/ext/*/mkmf.log || true
+    pushd $out/${ruby.gemPath}
+    rm -fv doc/*/*/created.rid || true
+    rm -fv {gems/*/ext/*,extensions/*/*/*}/{mkmf.log,gem_make.out} || true
+    rm -fvr cache
+    popd
 
     # write out metadata and binstubs
     spec=$(echo $out/${ruby.gemPath}/specifications/*.gemspec)